Aquaculture wastewater is rich in organic matter, nitrogen, phosphorus, and other nutrients that, if not properly treated, can cause severe environmental degradation, including water pollution and biodiversity loss. To address these challenges, researchers are increasingly turning to constructed wetlands as a sustainable and effective solution for wastewater treatment.
A recent study published in Microorganisms by researchers from the Institute of Subtropical Agriculture at the Chinese Academy of Sciences explores the performance of a multistage surface flow constructed wetland (SFCW) in treating aquaculture wastewater, with a particular focus on the role of epiphytic biofilms. The study provides valuable insights into how aquatic plants and microorganisms interact to remove contaminants and how these interactions are influenced by seasonal changes and different treatment processes.
Constructed wetlands for wastewater treatment
Constructed wetlands are engineered systems designed to mimic natural wetlands, utilizing aquatic plants, microorganisms, and artificial substrates to treat wastewater. These systems are particularly effective in treating high-flow or high-load wastewater, such as that generated by aquaculture operations. The multistage SFCW studied by the authors consists of six treatment ponds, each containing different species of aquatic plants and treatment processes, including aeration and biofiltration.
The efficient multistage treatment system integrates a sedimentation pond, a first filtration dam, an aeration pond, a second filtration dam, a biological filter pond, and a submerged plant stabilization pond, forming a comprehensive and ecological framework for wastewater remediation. The researchers established a demonstration site at a bullfrog aquaculture facility in the Datong Lake region of Yiyang City.
Key findings of the study
The study found that the multistage SFCW consistently achieved a total removal efficiency (TRE) of over 60% for various contaminants, including total nitrogen (TN) and total phosphorus (TP). This high removal efficiency highlights the potential of constructed wetlands to mitigate the environmental impact of aquaculture wastewater.
The aeration pond played a crucial role in enhancing dissolved oxygen levels, providing optimal conditions for phosphorus removal in July and nitrogen removal in November. Within the aeration pond and the biological filter pond, epiphytic bacterial α-diversity was significantly higher than in other treatment ponds, indicating that these areas offer an enriched microenvironment conducive to bacterial colonization and activity.
“This technology not only optimizes water purification processes in intensive aquaculture systems but also deepens our understanding of the synergistic interactions between aquatic plants and epiphytic biofilms, revealing their crucial functions in removing contaminants from bullfrog aquaculture wastewater,” said Professor Xie Yonghong from the Institute of Subtropical Agriculture.
Seasonal variations in treatment performance
One of the key findings of the study is the influence of seasonal changes on the performance of the SFCW. The researchers monitored the system during two vegetation periods: July, representing the peak growth period of aquatic plants, and November, representing the late growth period. The results showed that the system’s ability to treat TN became more stable over time, while TP removal efficiency was significantly higher in July compared to November.
The study also revealed that the aeration pond played a critical role in improving dissolved oxygen (DO) levels, which in turn enhanced phosphorus removal in July and nitrogen removal in November. This finding underscores the importance of aeration in optimizing the performance of constructed wetlands, particularly in systems treating nutrient-rich wastewater.
Epiphytic biofilms, composed of diverse bacterial populations attached to the surfaces of aquatic plants, play a crucial role in contaminant transformation processes within constructed wetlands. The study found that the diversity and composition of these biofilms varied significantly between the two vegetation periods and among the different treatment ponds.
In July, the abundance of Firmicutes, a bacterial phylum involved in sulfur metabolism, was notably higher, while in November, the abundance of Nitrospirota and Acidobacteria increased significantly. These changes in bacterial composition were linked to variations in functional genes associated with sulfur metabolism, nitrogen fixation, and oxidative phosphorylation, highlighting the adaptability of epiphytic biofilms to changing environmental conditions.
Implications for sustainable aquaculture practices
The findings of this study have important implications for the design and operation of constructed wetlands in aquaculture wastewater treatment. The integration of aeration and biofiltration processes can significantly enhance the overall performance of these systems, ensuring stable and efficient contaminant removal. Additionally, the study highlights the importance of considering seasonal variations when deg constructed wetlands, as system performance can be influenced by changes in vegetation periods and environmental conditions.
By optimizing the design and operation of constructed wetlands, aquaculture operators can reduce the environmental impact of their operations, contributing to the sustainable growth of the industry. Furthermore, the insights gained from this study can inform the development of more effective and efficient wastewater treatment models, not only for aquaculture but also for other industries generating nutrient-rich wastewater.
Conclusion
The study demonstrates the effectiveness of multistage constructed wetlands for aquaculture wastewater treatment, in which epiphytic biofilms play a crucial role in contaminant removal. The findings emphasize the importance of integrating aeration and biofiltration processes, as well as considering seasonal variations, in the design and operation of these systems.
“The synergistic interactions between aquatic vegetation and epiphytic biofilms are fundamental for enhancing nutrient removal and maintaining long-term system performance,” said Dr. Chao Chuanxin, the study’s first author. “From an application perspective, the strategic management of aquatic plants and continuous aeration are key technical interventions to maximize the potential of the ‘Four Ponds and Two Dams’ constructed wetland system.”
As the aquaculture industry continues to grow, the adoption of sustainable wastewater treatment practices, such as constructed wetlands, will be essential to minimize environmental impact and ensure the industry’s long-term viability.
XIE Yonghong
Institute of Subtropical Agriculture
E-mail: [email protected]
Reference (open access)
Chao, C., Gong, S., & Xie, Y. (2025). The Performance of a Multi-Stage Surface Flow Constructed Wetland for the Treatment of Aquaculture Wastewater and Changes in Epiphytic Biofilm Formation. Microorganisms, 13(3), 494. https://doi.org/10.3390/microorganisms13030494
Editor at the digital magazine AquaHoy. He holds a degree in Aquaculture Biology from the National University of Santa (UNS) and a Master’s degree in Science and Innovation Management from the Polytechnic University of Valencia, with postgraduate diplomas in Business Innovation and Innovation Management. He possesses extensive experience in the aquaculture and fisheries sector, having led the Fisheries Innovation Unit of the National Program for Innovation in Fisheries and Aquaculture (PNIPA). He has served as a senior consultant in technology watch, an innovation project formulator and advisor, and a lecturer at UNS. He is a member of the Peruvian College of Biologists and was recognized by the World Aquaculture Society (WAS) in 2016 for his contribution to aquaculture.
